The present invention relates to a method for operating a device to vary a blade setting angle, and a varying device as such.
Larger-sized wind power plants have a blade setting angle controller on the rotors. It adjusts a setting angle of the rotor blade to control the power and speed of the rotor. As a rule, setting ranges having a span of from 20° to 25° are employed here. The secondary function of the blade setting angle controller consists in bringing a rotor to a stop. To this end, the rotor blades are rotated up to a so-called feathering position at which a torque is no longer generated. This requires a setting range of about 90°.
A device for varying the rotor blade of a rotor on a wind power plant has become known from DE 101 40 793 A1, the entire contents of which is incorporated herein by reference. Here, the rotor blade is rotatably supported by a rotor hub via an antifriction bearing. The antifriction bearing has three bearing rings with two raceways two radially outer rings of which are joined to the rotor hub and a so-called tubular extender and a third ring runs internally with respect to the outer rings in a first aspect. The variation of the rotor blade and extender with respect to the rotor hub is provided by two variable drives one of which adjusts the angular position of the non-joined ring with respect to the rotor hub while the second drive adjusts the angular position of the rotor blade with respect to the non-joined ring. For a movement of the rotor blade to the desired angular position, the two drive systems are triggered, i.e. each of the drives runs at a predetermined variation rate for a time until the rotor blade has taken the desired angular position. To obtain a lubricant spread as uniform as possible inside the antifriction bearing during the variation of the blade setting angle we propose to operate both of the variable drives in opposed senses until the desired angular position is reached.
Using an antifriction bearing for the system for varying the blade setting angles, which technically is also referred to as a pitch system, has the disadvantage that it is necessary to overcome a breakaway torque of the antifriction bearing. The higher the wind speed is and, hence, the moments of strike and swivel from the rotor blade act onto the bearing the larger is the breakaway torque required to adjust the rotor blade. The breakaway torque occurs if a rotation starts from stoppage or if the rotational speed is lower than a critical speed which is close to zero. The critical rotational speed depends upon the configuration of the bearing and may be explained by a slip-stick effect between the antifriction bearing and the raceway. The slip-stick effect substantially is a transition from friction at rest to rolling friction on the bearing.
Since the breakaway torque in an antifriction bearing for varying the rotor blade position, due to its construction, distinctly is higher than are the driving torques necessary for the variation process the breakaway torque plays an important role in designing pitch drives.
It is the object of the invention to provide a method for adjusting the blade setting angle for a pitch system, and a device for varying a blade setting angle, which apply a much more uniform load to the bearings and tooth system on the rotary joint and avoid, or at least greatly reduce, stoppage marks in the bearing, and which can be designed to have a lower power output for the variable drives.